This is FRESH AIR. I'm Terry Gross. There's so much I have to learn each day in preparation for interviews that when I don't absolutely have to know something, I sometimes give myself permission not to learn about it. And that's been my attitude toward bitcoin until now. Or, to put it another way, when both Bjork and Microsoft are accepting bitcoin, it's time. So we're going to talk about what bitcoin is and how it's used in the underground and legit marketplaces, how it's become a vehicle for investors and how big banks are starting to copy it. My guest, Nathaniel Popper, is a technology reporter for The New York Times who's been covering digital currency. A couple of years ago he wrote a book about bitcoin called "Digital Gold." Nathaniel Popper, welcome to FRESH AIR. So for those of us who have never used bitcoin and don't really understand how it works, you tell me, why should we care?

NATHANIEL POPPER: Well, I think that there are a number of layers on which this bitcoin thing is interesting. I mean, on the most sort of immediate level, people are using bitcoin in really interesting ways. I think people are using it as a sort of black market currency to buy drugs and make ransom payments, and it is allowing for essentially new types of crime. But I think it also is pointing in the direction of where money might be going, and I think it tells us something about what money is. And then, you know, to zoom out even more broadly, I think it's really interesting because it's not just a new kind of software or a new kind of money. It is essentially a social movement. You know, it has taken off because it has won-over thousands, tens of thousands, millions of people around the world. And I think it's really interesting to think about what it is about this thing that has been so interesting to people.

GROSS: So just give us a sense of the scope. Like, how much money is invested in bitcoin now?

POPPER: Well, if you were to buy all of the bitcoin out in the world right now at the price this week, you would pay something like $120 billion. So that's the sort of simple way of thinking about the size of the bitcoin economy. That is, just for comparison's sake, larger than the value of Goldman Sachs or Morgan Stanley, larger than the value of PayPal. So that value is stored in something like 17 million bitcoins that are distributed around the world.

GROSS: OK. So what is a bitcoin?

POPPER: Well, to start with, and I think the thing that probably most people are aware of, it's essentially a digital token that you can buy and sell. But I think one of the reasons bitcoin has remained so confusing to people is that it's that digital token but then it's also the network on which it lives. And it's it's really the network that makes it so different. And so we refer to bitcoin, we refer to that network as essentially the bitcoin network. And it's something more like the internet. It's a decentralized network of computers around the world where all of these bitcoin live.

GROSS: So was it created to solve certain problems with money as we know it?

POPPER: Yes. I mean, this idea when it first emerged in late 2008, actually on Halloween of 2008, was the culmination of really decades of work among a sort of small group of computer scientists and activists who were worried about - their biggest concern was around privacy. They were really worried that, you know, in the existing system when money became digital. So when we started to be able to move money around on computers with credit cards, every transaction that you made was tracked and could later be monitored by the government or by big companies. And so, you know, a big part of the work that went into this was to essentially create an anonymous digital cash.

And so that was one strain of thinking that went into this. But the other big strain when this came out was that this was essentially two months after Lehman Brothers went bankrupt. So right in the heart of the financial crisis. And there was a lot of distrust of both Wall Street and the big banks, but also of central banks. And here this was introduced as a new form of money that could exist independent of all of these institutions that people were so skeptical of.

GROSS: So the people who created bitcoin, 'cause it grew out of a movement, wanted privacy. But I'm not sure exactly where the line is between privacy and secrecy, but there's been a lot of secrecy surrounding the use of bitcoin because the first place it really took off was the underground market, like, on the dark web, the black markets on the dark web selling drugs and sex, right?

POPPER: Right. For sure. I mean, the line between privacy and secrecy is always very, very fuzzy, and I think that a lot of the technologies that are out there to provide privacy are also sort of abused on the other side from people wanting to do things that they don't want the government to be watching. And so yes, I mean, bitcoin sort of came out of this idealistic impulse. And, you know, after it was announced by the creator of bitcoin, this character known as Satoshi Nakamoto, it sort of stumbled along for two years, and, you know, you could send bitcoin around, but they really weren't worth anything at that point. And it really kind of gained its first reason for being with the creation of the Silk Road, which was this, you know, online black market sort of eBay where you could buy drugs. And the Silk Road, the creator of the Silk Road realized that bitcoin made this possible for the first time. It was, frankly, quite hard to buy drugs online before this because if you did, the police would just go ask PayPal or Visa, you know, who had sent this money to buy this baggie of heroin or marijuana, and PayPal would give those records over and the person would get arrested. With bitcoin, you could send that money and nobody would know where the money came from, and that sort of gave rise to this whole new online market.

GROSS: And it's the same phenomenon with ransomware, when somebody's computer is basically being held hostage by malware, and the only way to get access to your computer back is to pay the designated amount of ransom money in bitcoin. But, of course, experts warn that even if you pay it, you might not necessarily get access to your computer again. But - so that's something that's caught on.

POPPER: Yeah. I mean, that's been a big thing that's risen up in the last two years, and...

GROSS: And I should say that applies not just to individual computers, but also to, like, whole networks and to hospitals and, you know, around the globe.

POPPER: Yeah. I mean, it's created enormous problems for companies, for governments. You've seen, yeah, hospitals that have had to just go back to analog recordkeeping for weeks. I think it was the San Francisco Chronicle, or maybe it was a radio station here that basically had to stop using computers because their computers were all frozen by a ransomware attack. And ransomware was really something that existed before bitcoin. But, you know, in tech speak, it didn't scale without bitcoin. Before, somebody would have to go get a money order and send it around the world physically. That's not an easy thing to do. With bitcoin, you can now send, you know, $500 to the captor of your files in the Ukraine or Russia, and the transaction is done in 20 minutes. And, you know, that is possible because of this new way that bitcoin works, which, you know, the first sort of real-world uses of that have not been altogether positive ones for the world, I think.

GROSS: In terms of the dark web and the illegal, you know, the markets for illegal goods on the dark web that you have to pay for with bitcoin, some of those sites have been shut down, including Silk Road, the one that you mentioned, and more legit uses of bitcoin are emerging now. So what are some examples of that?

POPPER: Well, the idealism that fueled bitcoin at the beginning, the place where you've seen that playing out is in countries where people have their money trapped or are losing money because the local currency is, you know, is experiencing hyper inflation and so people are losing all of their savings and looking somewhere outside of the government's control to put money. And so you've seen that in countries like Venezuela and Argentina. You even hear about it in Zimbabwe. You know, in those places, people have always clamored to exchange their local currency for dollars because dollars were so much more reliable, but there was, you know, a real shortage of dollars. And when you got the dollars, you frequently had to sort of put them under your mattress, which wasn't terribly secure. You know, the vision with bitcoin is that in those sorts of places, you can now trade your local currency for bitcoin and have a somewhat more stable place to keep your money then, you know, the bolivar or the Argentine peso.

So that's sort of, I think, one place where people like to talk about - talk up, bitcoin aficionados like to talk up. I mean, it's also very easy to sort of move money around the globe so, you know, it takes a long time right now to make a sort of pretty basic bank transfer to India, to China. You know, that can take weeks and, you know, require sort of fees at every step along the way. The idea with bitcoin is, you know, you can send it right now and it's there in essentially 10 minutes. And the person can log in and they don't have to get approval from anybody. You know, that's particularly attractive in countries where it's hard for people to get bank accounts and where, you know, places like India, again, or Africa, where people are sort of locked out of the online economy because they can't get a credit card, they can't get a debit card. You know, they can't sign up for Netflix. Now you can sign up for Netflix very easily in India or Africa, even if you don't have a credit card, thanks to bitcoin.

GROSS: We need to take a short break here so let me reintroduce you. If you're just joining us, my guest is Nathaniel Popper, and we're talking about bitcoin. He's been writing about digital currency for several years. He's a tech reporter at The New York Times, and a couple of years ago, he wrote a book about bitcoin called "Digital Gold." We'll be right back. This is FRESH AIR.

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GROSS: This is FRESH AIR, and if you're just joining us, we're talking about bitcoin and other digital currencies. And my guest, Nathaniel Popper, has been writing about bitcoin for several years. He's a tech reporter for The New York Times and the author of a book about bitcoin called "Digital Gold." So I'm not sure we know who invented money, but we do know who invented bitcoin. Except we don't know because...

POPPER: (Laughter).

GROSS: (Laughter) Because...

POPPER: That's a good way of putting it.

GROSS: Yeah. It's a pseudonym. He never really revealed who he was. Even you, who have been covering this for years, don't know who he is.

POPPER: Right.

GROSS: I'm sorry. Yeah. I don't even know it's a he, right?

POPPER: I was going to say that. So people frequently say he, she, they or it in case it is a sort of autonomous, you know, being that created this of some sort. But, you know, what we do know is that the person who first introduced this back in 2008 and then released the first software a few months later went by the name of Satoshi Nakamoto and communicated essentially only by email, would get on sort of chats and sort of social media forums, but always under that Satoshi Nakamoto pseudonym. And a few years into bitcoin's existence, right as it was beginning to take off, Satoshi essentially signed off and disappeared, you know, sent the last email, gave control of the system over to the people who had been drawn to it and were, you know, working on the software at that point. And since then there's been a sort of manhunt for, you know, to discover the true identity of Satoshi Nakamoto.

And a bunch of names have been floated over time. I wrote a story when my book came out about the person who - one of the people who was widely viewed as the most likely candidate. But all of the people who have been, you know, fingered as potential Satoshi Nakamotos have denied essentially that they are, except for, I should say, one person who claimed to be Satoshi Nakamoto and won over a certain number of people. This got a lot of news, I think, maybe a year or two back, this guy named Craig Wright from Australia who claimed that he was Satoshi. But as people looked into it and looked into the sort of electronic records - it was quite a chase - I think most people concluded that this was not in fact Satoshi Nakamoto.

GROSS: So when Satoshi Nakamoto, whoever that is, started bitcoin, he or she issued something between, like, guidelines and a manifesto. Like, a nine-page document. Can you sum up, for those of us who don't really understand this (laughter), the principles that were laid out in those nine pages?

POPPER: Sure. Yeah, so this was the original. It's called Satoshi's White Paper. You know, it has this sort of iconic status, this nine-page PDF that was released in early - in late 2008. And it sort of described how this system was going to work. And it said it would be a sort of electronic cache, and there were going to be certain rules that would govern this electronic cache. There would only ever be 21 million bitcoins created. That rule was sort of stated there at the beginning. And that was created so that it would have a sort of scarcity like gold and - which might lead people to think there was going to be a value in it. If there wasn't going to be an unlimited number of them, that might confer a certain value on bitcoin, which it has ended up doing. So that was one rule.

The other rules were about how Bitcoin would be distributed. It's not - there wasn't going to be a bank of bitcoin that would distribute them to everybody. They were going to be sort of slowly dripped out over time to people who joined the network. And I think that's the most important thing about the rules around bitcoin was that it was going to be a network of computers, sort of like the Internet, that anybody could join and anybody could support this. And that would allow for bitcoin to exist independent of any sort of central source of authority. There wasn't going to be a government here. There wasn't going to be a company. There was going to be this network of computers that was supporting it, and that means that anybody can join that network and send money to anybody else. And so those were sort of the basic rules that were laid down.

And I should say that in the first months after this was proposed, this was not a rousing success. There were, you know, a handful of people, you know, maybe eight people who responded to this idea. Most of whom thought that there was no way that it could work.

GROSS: Well, for this to work, it really requires a level of faith. When you're talking about, say, dollars, it's backed up by the U.S. government. And if you have money in a bank, a certain amount of it is backed up by the FDIC. You know, if you invest in the stock market, it's going to fluctuate, but you have shares in something whereas with bitcoin it just seems like an act of faith in bitcoin.

POPPER: Well, you are certainly right. I should note I think that, you know, all of those instances you just mentioned - the U.S. dollar is backed up by the U.S. government, by the FDIC - that's true. I mean, if you kind of dig a little deeper, you know, what you're expressing faith in when you express faith in the dollar is essentially the U.S. government and the FDIC. You're believing that those are going to be around. And obviously, that's not maybe a hard thing to believe in, but there's some chance that it won't happen. And certainly there are countries where the government has issued currency and then the government has fallen and the currency has turned out to be worthless.

So to a degree, money is always about faith. It's about believing that the thing you're holding in your hand is going to be worth something tomorrow, next week, in a month and that somebody will take it and give you something in exchange. The same is true with bitcoin. And certainly, there are not the institutions backing it up that you have for the U.S. dollar or for stocks. But what is backing it up is this network. And so you in essence are sort of expressing your faith in that network and the power of the network and the power of the rules behind bitcoin to draw people to this currency and to make people think that the network, you know, may outlive the U.S. government. I wouldn't argue that myself. I don't know the odds. I would say probably the odds of the U.S. government outlasting the bitcoin network are good.

But I think that a lot of people have - had assumed that bitcoin - that the bitcoin network wouldn't survive to, you know, through the first year, much less the first eight years, which it's done. And it's sort of continued to kind of engender this faith among the people who believe in it, who follow it.

GROSS: My guest is Nathaniel Popper, a tech reporter for The New York Times and the author of a book about bitcoin called "Digital Gold." After we take a short break, we'll talk more about how the bitcoin system works and how bitcoin are created by huge server farms competing against each other. And David Edelstein will review the new movie "Three Billboards Outside Ebbing, Missouri" starring Frances McDormand. I'm Terry Gross, and this is FRESH AIR.

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GROSS: This is FRESH AIR. I'm Terry Gross. We're talking about bitcoin, the digital currency that was created in 2008. Although its roots were in idealism and libertarianism, it first became widely used for purchases on the dark web, the sites on the Internet black market selling drugs and sex. But this digital currency is now being used for more mainstream purchases. Big banks are starting to find uses for some of the innovative structure of the bitcoin system. My guest, Nathaniel Popper, is a tech reporter for The New York Times. A couple of years ago, he wrote a book about bitcoin called "Digital Gold."

So when bitcoin was first released into the world, it was determined by the person who released it, who goes by the name Satoshi Nakamoto, he or she determined how much bitcoin there would be in this world. There's a finite amount of bitcoin that will ever be released to make sure that, like gold, it retains its value. So it's a kind of complicated process how bitcoin is created or mined. Mined is the word that's used. New bitcoin is mined. So would you just tell us a little bit, like, in a comprehensive way about how new bitcoin is mined?

POPPER: It's a dangerous question, and it's a hard one to answer simply, but, you know, the answer to how bitcoin are created does sort of give you some glimpse into the inner workings of how this thing functions and why it has survived as long as it has. I mean, essentially, bitcoin released onto the network every 10 minutes. A new block of bitcoin is released onto the network every 10 minutes. And this started on the very first day. On the very first day, there was zero bitcoin in the world. And after 10 minutes - after about 10 minutes, 50 bitcoin were released to one of the computers that was hooked into the network, which at that point was Satoshi Nakamoto's computers. They were almost the only computers that were hooked in at that point. But the rules of bitcoin - the software determine how those bitcoins, those new bitcoins being released, are going to be distributed to people.

And the first thing that this does is that it encourages people to join the network. You can essentially - at least early on, you could essentially get free bitcoin if you joined the network. And so it incentivized people to join the network. The other thing it did was that it got those computers to start keeping the records for the network. So if you want to win those bitcoins, essentially you have to start working as an accountant for the network and registering all the new transactions that come in. And if you are doing that - the more computers you add to help, you know, serve as accountant for the network, the better chance you have of winning bitcoins. And so that is how sort of the records are kept, and that's how you get people to volunteer to keep the records. You give them new bitcoins. You offer these new bitcoins. So over time, that incentive system has generated this enormous network.

Right now, there's something like 13,000 nodes or computers hooked into the network that are helping to keep these records. And a lot of those are mining, trying to win these new bitcoins. And so this complicated economic system was set up with lots of incentives in there to get people to participate and to sort of create the foundation for this decentralized network to keep all the records.

GROSS: So you can't just say, well, I want to create new bitcoin. It's a kind of interesting process. You're basically competing with other people who also want to create new bitcoin. So what do you have? Do you have, like, a lot of computers competing with each other? And what's the competition? Like, what are the...

POPPER: Yeah.

GROSS: Who decides who wins?

POPPER: You know, we're slipping down the rabbit hole here and I...

GROSS: Yeah, that's what I was afraid of, but...

POPPER: Let's make sure not to go...

GROSS: Yeah.

POPPER: Let's make sure not to go too deep data because it's based on cryptography and encryption, which is sort of the leading edge of math, you know, basically really hard math problems you have to solve. But at the most basic, computers are trying to process all the transactions coming into the bitcoin network as quickly as possible. And the faster you do it, the more efficiently you do it, the better chance you have of winning bitcoin. There's an element of luck in it. It's somewhat like a lottery, but essentially the person with the most computing power has the best chance of winning the lottery.

And so what's that - what that's created today is a world in which you have literally server farms in outer - inner Mongolia, in Tibet, in Iceland. Anywhere where you can get cheap electricity to run computers very fast, people have set up basically server farms, big, you know, buildings just filled with computers trying to sort of unlock these new bitcoins but also sort of serving as the backbone of this network. And, you know, the more computers you have joined in, the more secure the network is, the harder it is to attack. And it's this crazy world in which - I mean, literally in China, which has become one of the most, you know, one of the places where you have the most bitcoin mining, you know, spread all around China, you have next to - you know, next to hydroelectric dams and next to a coal plants, people have set up these server farms that are dedicated to doing nothing but mining bitcoin.

GROSS: I know you visited a server farm in Iceland. Did you go to one in China, too?

POPPER: I went a couple years ago to one in China. They have gotten a lot bigger and more sophisticated since then. I mean, there are literally sort of towns that are built around this in China where you have people just living in the bitcoin mining facility, you know, Chinese people who really - you know, the people who are working there are sort of the custodians. They - most of them have no idea really what's going on or how the system works. But it's - you know, it's created this whole economy.

GROSS: So bitcoin is being used as an investment vehicle in the U.S. It's being used for investing, in speculation. How is that playing out here?

POPPER: Well, very well for the people who bought it early on. I mean, a bitcoin this week is worth something like $7,500. You know, a year ago, it was worth less than $1,000. And that has attracted a whole bunch of new people to this. It's attracted people around the world. Here, what you've seen is a lot of hedge funds getting into this game. So there are now hedge funds being set up. Something like 100 hedge funds in the last year have been set up to invest exclusively in virtual currencies, bitcoin as well as some of the competitors that have sprung up.

GROSS: Wow. Well, say this is a bubble, what happens (laughter)? I mean, like, the price of bitcoin has been shooting straight up, but things that go up sometimes come back down.

POPPER: Yes. I mean, if you look at the chart of the bitcoin price since it was born, it is just a series of spikes and then drops, and then spikes and then drops. And over time, you know, you get the spike, and it drops down to a level that is generally still higher than where it was before the spike, but lower than the spike. And so I think a lot of people are asking right now how long this can go on. And certainly, you've heard numerous CEOs of banks say, this is unsustainable; this is a bubble; this is going to crash.

And I think there's no doubt that there probably is going to be some reckoning here. I mean, this meets many of the definitions of a bubble. People are speculating on the future value and desire for bitcoin. People are speculating that this will serve more purposes in the future and will be more valuable to more people in the future than it is today. And they're betting - a lot of people are just betting that the price is going to go up without knowing anything about it. And those are a lot of the characteristics that you see in bubbles.

I mean, you know, the counterargument is that this is the first time that we've had a scarce digital resource. So I - the Internet, until now - most things on the Internet, you can copy and paste, right? That's what the music industry found. You can copy and paste an MP3. You can copy and paste a movie file. Things aren't scarce on the Internet, and one of the things that bitcoin did through this weird, complicated system of incentives is, it created a scarce digital asset for the first time.

So a lot of people think about this now as something like digital gold. You know, this is a place where you can keep your money because there's only going to be so many of them, and the system works, and it's in some ways better than gold because, you know, gold, you can't carry across a border secretly. You can't - you can try to stuff it in your underwear.

But, you know, gold, people can - it's hard to travel with gold. Bitcoin - as long as you have that password, you can go somewhere else with internet access and you have access to your money. So that's the sort of thesis on this. But I think that the sort of expectations and the types of people who are getting into this right now, a lot of them are not terribly sophisticated.

GROSS: So of the maximum 21 million bitcoin that can be released by - what were - year was it, 2040?

POPPER: 2140, yeah.

GROSS: 2140, right - oh, 21 - wow, 2140.

POPPER: We got a while.

GROSS: Wow.

POPPER: We're talking about a distant future.

GROSS: I'm hearing, like, 2040. That's, like - that's so far away.

POPPER: It is.

GROSS: OK, so how many bitcoin have already been released?

POPPER: We're getting close to 17 million. So the reward to people who are helping to support the network falls in half every four years. So initially, it was 50, and then 25 and now we're down to 12 1/2, and it'll sort of keep going down like that until it approaches zero. And I think, obviously, part of the idea is, they will be worth more, so the 12 1/2 that are released now are actually worth a lot more than the 25 that you were getting a year ago.

GROSS: OK, it's time for a short break. Let me reintroduce you. My guest is Nathaniel Popper. We're talking about bitcoin, and he's been writing about bitcoin for several years. He's a tech reporter for The New York Times who wrote a book a couple of years ago about bitcoin called "Digital Gold." Back after this short break - this is FRESH AIR.

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GROSS: This is FRESH AIR. And if you're just joining us, my guest is Nathaniel Popper. He's a tech reporter at The New York Times. And we're talking about bitcoin - digital currency - and he's been covering bitcoin for several years. A couple of years ago, he wrote a book about it called "Digital Gold."

So, you know, whether you use bitcoin or not, whether you think it's going to last or not, the architecture of the system seems pretty ingenious. And there are major banks and even the New York Stock Exchange, you know, that are picking up on some of the architecture to borrow it for their own purposes, and what they're borrowing from is what's called the blockchain. Would you explain what that is and how, like, major banks are trying to borrow that system?

POPPER: Sure. Well, I think the blockchain, in the simplest sense, is the record of all the bitcoin transactions. It's a ledger, a sort of a spreadsheet on which bitcoin transactions are recorded. But what's special about the bitcoin ledger - the bitcoin blockchain - is that it's not kept by a central institution. It's kept by a bunch of people, and part of the idea is that it's a bunch of people who don't trust each other but can use this system to have a sort of shared record of their assets.

And so this blockchain idea, this idea of keeping records in a decentralized way so that anybody can consult it and that nobody is in charge - that idea of the blockchain is something that's piqued a lot of interest in the financial industry but also in a whole bunch of other industries. IBM has made this one of their biggest pushes over the last few years to kind of try to regain relevance. They have made a big move into the blockchain industry, as has Microsoft. And they're essentially making a bet that this is a new way to track information.

And, you know, we live in an information economy, and so if you can come up with new ways to track and store information more reliably, it has the potential to recreate some of the foundations of the information economy. It really sounds rather vague.

You know, when you just look at something like the financial industry, the banks are looking at this as, you know - maybe instead of paying the New York Stock Exchange to buy and sell stocks there, and then transfer the money for us, and move the stocks back and forth and make sure all the records are kept, maybe we - all the banks - we can just set up a blockchain where we can all trade, and we don't have to pay anybody in the middle, and we can keep track of all those records, and all of us can do it without trusting any of the other people in the system. And that's the sort of basic idea that I think has given rise to this whole new industry.

GROSS: So you're not allowed to invest in bitcoin because you cover it for The New York Times. Are you allowed to use it, and have you used it?

POPPER: Yes. I mean, our take at The New York Times has basically been, I can have enough to play with and understand it. And I think the understanding has generally been that, you know, those bitcoins essentially belong to The New York Times so that I don't get any big ideas.

But yeah, I mean, I'm in there on a daily basis trying to understand how these things work, how you move between different currencies, how it can move around the world. And that's been an important part of reporting on this.

GROSS: So if you want to get bitcoin to make purchases, how do you get it?

POPPER: Well, companies - not surprisingly, companies have sprung up to make this very easy for you to take your money and give you bitcoin. You know, there's - probably the biggest company in the United States is a company called Coinbase, which is essentially a sort of Charles Schwab or an E-Trade for bitcoin. You send them money, and then you can trade on their platform. You can move in and out of bitcoin. And then you can take your money out and transfer it back to your bank.

And they've made it very easy so that anybody - you know, so it's as easy as - probably easier than buying a stock is through E-Trade. And part of what's interesting there - I guess that's not too surprising. What's interesting is that the government and regulators have essentially allowed this to happen, have said, this is OK.

New York - state of New York has created a BitLicense that Coinbase has, and that makes it easier for them to do this and easier to get bank accounts. And so at least in the United States, the government has sort of said, we're going to let this happen; we realize there might be something of value here, so we're not going to try to kill this.

GROSS: Have you had any great bitcoin adventures in researching your book or writing for The New York Times that you could share for - share with us?

POPPER: I mean, this whole thing has been such an incredible story. I mean, that's why I was drawn to it. I mean, the number of people who have gone to jail - often shortly after getting fabulously wealthy - is incredible. And so a lot of the stories I talk - tell in my book are these stories of these astronomic rises followed by these incredible falls. And oftentimes, I was there.

You know, I - you know, one of the main characters in my book, I met him in this bar that he had essentially bought a piece of using bitcoin and where he would have these bitcoin parties, where he met his girlfriend. You know, they took bitcoin for - the waiters and waitresses took bitcoin. And he was on top of the world. He had just come back from Argentina. He was traveling around. A week later, he got stopped at the airport by the police, went to trial, ended up in jail. And, you know, I was talking to him at every stage along the way.

And I've had that experience in so many different realms - you know, in Iceland, in China, in Argentina. And just to see the way that this technology has created these little universes of - it's only - they're like little science fiction cells where these people are imagining these new futures, and, you know, in each place - in China, Argentina, everywhere you go - it has evolved in different ways.

And so just to see the way that this software, you know, it - that this piece of program that this anonymous person wrote - the way it can sprout up and create all these things in the real world - you know, going to these gorges in China where there are now people just living in these enormous industrial sites, working on this - it's - that's, I think, what's been the most incredible to see.

GROSS: Well, Nathaniel Popper, I want to thank you so much for talking with us.

POPPER: Thank you so much for having me.

GROSS: Nathaniel Popper is a tech reporter for The New York Times and the author of a book about bitcoin called "Digital Gold." After we take a short break, David Edelstein will review the new movie "Three Billboards Outside Ebbing, Missouri." This is FRESH AIR.